1. Field of the Invention
The invention relates to an air mattress, more particularly to an air mattress which can be manufactured at a reduced cost.
2. Description of the Related Art
FIG. 1 illustrates a conventional air mattress 1 which includes an upper sheet 11, a lower sheet 13, and a surrounding sheet 12 interconnecting the upper and lower sheets 11, 13. An upper edge 121 of the surrounding sheet 12 is sealed to four sides of the upper sheet 11. A lower edge 122 of the surrounding sheet 12 is sealed to four sides of the lower sheet 13. The upper sheet 11 has a top surface adapted to be in contact with the body of a user. To provide a comfortable feeling of touch, the top surface of the upper sheet 11 is pre-treated, such as by printing, by attaching with fabrics or by planting tufts thereon. However, a pre-treated plastic sheet, such as a tufted plastic sheet, has a significantly higher cost of material than a non-treated plastic sheet. In the conventional air mattress 1, the upper sheet 11 has a size generally identical to that of the lower sheet 13. The cost of material for manufacturing the air mattress 1 is relatively high.